Long term hodlers who haven't locked their coins into staking can respond quickly to network events such as Bitcoin-cash. People who are running mining businesses can at least sell the business if they suddenly need access to a lot of capital. With proof of stake, it really is locked up for whatever period of time.
If your staking period is just a couple of weeks, this is probably less significant than owning a mining farm. But if your staking period is several months, the opportunity cost probably is greater than mining or hodling, because you sacrifice a lot in terms of flexibility.
When you put it that way, I expect to see a secondary market for stake. This could be implemented by selling the private key or by delegation similar to a mining pool.
Selling the private key would be a bad idea since you can't guarantee the seller destroys it. But you could have the staker address be a contract, with an ownership that can be transfered.
You could use an HSM to hold the private key and then sell the HSM. Overall it's still a bad idea to buy an HSM because you don't know what other transactions have been signed, but maybe the HSM keeps a history of everything it has signed as well.
Which, if you can still sell your staked coins, what is the point of locking them up in the first place?
If your staking period is just a couple of weeks, this is probably less significant than owning a mining farm. But if your staking period is several months, the opportunity cost probably is greater than mining or hodling, because you sacrifice a lot in terms of flexibility.